1. Field of the Invention
The invention relates to the field of electronic devices, and in particular, to a method and structure for accurately and neatly assembling a card-type electronic apparatus.
2. Related Art
A card-type electronic apparatus (such as a flash memory card or a PCMCIA card) is a computer component that can be used, for example, as a storage element, a communications interface, or an authentication device. A card-type electronic apparatus typically includes a small printed circuit board assembly (PCBA) encased in a durable housing. The PCBA can include various types of integrated circuits (ICs), such as flash memory or communications controllers.
The form factors of the different card-type electronic apparatus housings are typically defined by a formal specification that provides detailed size, shape, and connectivity requirements. Card-type electronic apparatus housings must therefore be carefully controlled to ensure compatibility with related products.
A card-type electronic apparatus is typically formed in a sandwich fashion, with two rigid plastic device covers enclosing the PCBA. Typically, those plastic covers are ultrasonically welded together, thereby ensuring a permanent encapsulation of the PCBA.
FIGS. 1A and 1B depict a conventional assembly process for a standard Secure Digital (SD) card 100. This process is similar to that described in U.S. Pat. No. 6,381,143, issued to Nakamura on Apr. 30, 2002. In FIG. 1A, an upper cover 110 is positioned above a lower cover 120. A PCBA 130 (that includes an IC 131 mounted on a PCB 132) is affixed to upper cover 110. PCBA 130 includes an IC 131 mounted on a printed circuit board (PCB) 132.
Upper cover 110 includes upper sidewalls 111 that run along the perimeter of upper cover 110. Multiple ultrasonic bonders 141 are mounted on mating surfaces 119 of upper sidewalls 111. Upper sidewalls 111 are sized and positioned such that mating surfaces 119 match up with corresponding mating surfaces 129 on lower sidewalls 121 that run along the perimeter of lower cover 120. Ideally, when upper sidewalls 111 and lower sidewalls 121 are clamped together and ultrasonic vibrations are applied to bonders 141, upper cover 110 and lower cover 120 are permanently joined to form a rigid enclosure for PCBA 130, as shown in FIG. 1B.
Unfortunately, the SD card 100 formed using conventional upper cover 110 and lower cover 120 can exhibit problematic deviations from the optimal SD card form factor. For example, because upper sidewalls 111 and lower sidewalls 121 must be aligned using a die (jig) or some other external alignment mechanism, misalignment can occur between upper cover 110 and lower cover 120. This misalignment can increase the overall width W1 of SD card 100 and cause SD card 100 to not fit properly into all SD card sockets.
Furthermore, because the height Hi of SD card 100 is determined by the combined heights of upper sidewalls 111 and lower sidewalls 121 (and any residual bonding material between the two), accurately achieving a specific value for height Hi can be difficult. In addition, the flow of bonders 141 as they melt during the ultrasonic joining process can cause form factor problems. Because joining occurs at an external seam of SD card 100 (i.e., mating surfaces 119 and 129 form a joint on the exterior of SD card 100), bonder overflow 142 can reach the exterior of SD card 100. This bonder overflow 142 can then harden, and like misalignment between upper cover 110 and lower cover 120, can cause fit problems for SD card 100.
What is needed is a card-type electronic apparatus housing that ensures good form factor integrity.